1. Field of the Invention
The present invention is directed to a stereo x-ray installation, and in particular to a stereo x-ray installation including means permitting guiding of a radiation-opaque instrument with respect to an examination subject.
2. Description of the Prior Art
Stereo x-ray installations are known which in general include two spaced x-ray sources having respective central rays intersecting in an exposure plane in an examination subject, an x-ray image intensifier video chain including an x-ray image intensifier having an input luminescent screen on which the image is generated by the two x-ray sources appear in chronological succession, a video camera for recording the output images from the image intensifier and generating video signals therefrom, and storage means connected to the video camera for storing the video signals of the stereo images for reproduction through a stereo viewer. Additional stages are sometimes disposed between the storage means and the stereo viewer which permit position-variable signals, generated by a signal generator, to be superimposed on the output signal of the storage means. Such stereo x-ray installations are used to generate three-dimensional x-ray images in transillumination.
One such stereo x-ray installation is disclosed in U.S. Pat. No. 4,485,815 which is used to supervise percutaneous puncture of an examination subject. The instrument used for the percutaneous puncture is a ruler-like carrier having a centrally disposed needle or catheter. To avoid direct x-ray irradiation of the hands of the surgeon, the carrier has a handle permitting it to be grasped outside of the radiation field. The needle or catheter is aligned to point in the direction of propagation of the x-rays. Although the direction of the needle incision can be seen, a precise alignment of the paracentesis channel is only possible by pivoting the x-ray diagnostics installation. The paracentesis depth, however, cannot be ascertained.
An x-ray installation permitting more precise identification of the three-dimensional arrangement of the patient and instrument is disclosed in German OS No. 30 06 749. In this stereo x-ray installation a television picture is reproduced with the two x-ray sources being controlled such that the two exposures which form a stereo image pair are generated with a slight time difference. The exposures are read in a known manner by a television camera, and are intermediately stored in respective image memories. Subsequently the stored image pair is reproduced on two picture tubes, having respective images separately supplied to each eye of an observer. A disadvantage of this apparatus is that the surgeon is not always in a position to recognize the resulting paracentesis channel with the required precision merely from the visual impression of the needle placed on the skin, because this is only partially visible at the edge of the stereo image.
German OS No. 29 36 259, corresponding to U.S. Pat. No. 4,346,717, discloses an installation for catheterization of organs wherein a guide mechanism for a needle is attached to an ultrasound device. The connection between the needle and the ultrasound device is such that a guide beam identifying the paracentesis direction is mixed with the ultrasound image dependent on the image of the guide channel. Again, however, a precise identification of the incision location is not possible because the representation is only two-dimensional. Moreover, the surgeon does not have complete freedom of movement during the procedure. The surgeon must hold the ultrasound array to which the guide is attached, and must then introduce the needle into the guide, after alignment of the needle, must introduce the needle into the patient. As with the aforementioned devices, a precise identification of the paracentesis depth is not possible.